Generated by SassMeister.com.

SassMeister-output.css

/* how wide should the windows/screens be? */
.convo {
  background-color: #eeeeee;
}

.bubble {
  background-color: #fafafa;
  color: #333333;
}

.metadata {
  color: #cccccc;
}

.incoming .bubble {
  background-color: #ffffff;
}

.sms .bubble {
  border-color: #64a926;
}

.push .bubble {
  border-color: #3a7ef2;
}

.sending .bubble {
  opacity: 0.7;
}

.key-exchange {
  padding-bottom: 1em;
}
.key-exchange div {
  margin-top: 2em;
  height: 1em;
  padding-bottom: 1em;
  border: 1px solid #ddd;
  border-width: 1px 0;
  font-size: 0.5em;
  text-align: center;
  vertical-align: top;
  text-transform: uppercase;
  color: #aaa;
}
.key-exchange div .lock {
  background: url(https://raw.github.com/WhisperSystems/TextSecure/master/res/drawable-hdpi/icon_lock.png) no-repeat;
  background-position: center 40%;
  background-size: 60%;
  display: inline-block;
  width: 4em;
  height: 4em;
  border-radius: 4em;
  border: 1px solid #ddd;
  margin: -1em 1em 0;
}

/* Style variants */
.green-stripe {
  border-top: 0.3em solid #64a926;
}

.blue-stripe {
  border-top: 0.3em solid #3a7ef2;
}

.green-background {
  background: #64a926;
}

.light-green-background {
  background: #d9e6cf;
}

.blue-background {
  background: #3a7ef2;
}

.yellow-background {
  background: #fff6df;
}

.light-blue-background, .encrypted.msg, .key-exchange, .key-exchange div .lock {
  background-color: #dfe8f7;
}

.bluish {
  background-color: #d0d0da;
}

/* Formatting */
.msg-text {
  display: block;
  padding: 0.5em 0.6em 0em;
}

.metadata {
  display: block;
  font-size: 0.70em;
  padding: 0.2em 0.6em;
}

.convo {
  width: 480px;
  font-family: sans-serif;
  font-size: 20.36364px;
  line-height: 1.2em;
}

.avatar {
  display: inline-block;
  background: url(https://whispersystems.org/assets/header/raven-46e547e5d71484be52060be1155f6ff2.png) 30% 10%;
  background-size: 200%;
  width: 53.81818px;
  height: 53.81818px;
  border-radius: 53.81818px;
  float: left;
}

.bubble {
  position: relative;
  border-radius: 4.36364px;
  max-width: 75%;
  border-bottom: 2.25px solid #dddddd;
}

.incoming .bubble {
  float: left;
}
.incoming .bubble:after {
  content: '';
  display: block;
  position: absolute;
  width: 0;
  height: 0;
  top: 1em;
  left: -0.8em;
  border-right: solid 0.5em #ffffff;
  border-top: solid 10px transparent;
  border-left: solid 0.4em transparent;
  border-bottom: solid 10px transparent;
}

.outgoing .bubble {
  float: right;
}
.outgoing .bubble:after {
  content: '';
  display: block;
  position: absolute;
  width: 0;
  height: 0;
  top: 1em;
  right: -0.8em;
  border-left: solid 0.5em #ffffff;
  border-top: solid 10px transparent;
  border-right: solid 0.4em transparent;
  border-bottom: solid 10px transparent;
}

.outgoing .bubble, .outgoing .metadata {
  text-align: right;
}

.msg {
  padding: 0.3em 11.63636px;
}

.msg:after {
  content: '';
  display: block;
  height: 0;
  clear: both;
}

/* android elements */
.notification-bar {
  background: url(https://whispersystems.org/blog/images/textsecure2-imessage.png) no-repeat;
  background-size: 100%;
  width: 480px;
  height: 34.28571px;
}

.header-bar {
  background: url(https://whispersystems.org/blog/images/textsecure2-imessage.png) no-repeat;
  background-size: 100%;
  background-position: 0px -34.90909px;
  height: 62.47619px;
  width: 480px;
}

.entry-bar {
  background: url(https://whispersystems.org/blog/images/textsecure2-imessage.png) no-repeat;
  background-size: 100%;
  background-position: 0px -789.81818px;
  height: 64.7619px;
  width: 480px;
}

.checkmark {
  display: inline-block;
  background: green url(https://github.com/WhisperSystems/TextSecure/blob/master/res/drawable-mdpi/check.png?raw=true) center;
  background-size: 90%;
  width: 1em;
  height: 1em;
  border-radius: 1em;
  border: 0.15em solid #ffffff;
  margin: 6% 62%;
}

/* debug styles */
/*
.convo { border: 1px solid red; }
.msg { border: 1px solid blue; }
*/

SassMeister-rendered.html

<div class='notification-bar'></div>
<div class='header-bar'>
  <!--<span class='checkmark'></span>
  -->
</div>

<div class='convo'>
    <div class='incoming sms msg unencrypted'>
      <span class='avatar'></span>
      <span class='bubble'>
        <span class='msg-text'>This is a plaintext SMS. Unencrypted conversations are always SMS and have a plain jane, neutral gray backdrop.</span>
        <span class='metadata'>Feb 6</span>
      </span>
    </div>
    <div class='outgoing sms msg unencrypted'>
        <span class='bubble'>
            <span class='msg-text'>SMS shows a touch of green, like the money they'll cost you (if you're American).</span>
            <span class='metadata'>1:42pm</span>
        </span>
    </div>
    <div class='key-exchange'><div>Secure <span class='lock'></span>Session</div></div>
    <div class='incoming sms msg encrypted'>
        <span class='avatar'></span>
        <span class='bubble'>
            <span class='msg-text'>Blue skies, all is well. This SMS is encrypted.</span>
            <span class='metadata'>1:52pm</span>
        </span>
    </div>
    <div class='outgoing sms msg encrypted'>
        <span class='bubble'>
            <span class='msg-text'>Blue for security, green for SMS.</span>
            <span class='metadata'>1:36pm</span>
         </span>
    </div>
    <div class='incoming push msg encrypted'>
        <span class='avatar'></span>
        <span class='bubble'>
            <span class='msg-text'>Push messages are always secure, so they are extra blue.</span>
            <span class='metadata'>1:56pm</span>
        </span>
    </div>
    <div class='outgoing push msg encrypted'>
        <span class='bubble'>
            <span class='msg-text'>Plus they're free as in freedom, beer, and bird.</span>
            <span class='metadata'>1:56pm</span>
        </span>
    </div>    <div class='sending outgoing push msg encrypted'>
        <span class='bubble'>
            <span class='msg-text'>Not sent yet...</span>
            <span class='metadata'>2:46pm</span>
        </span>
    </div>
</div>

<div class='entry-bar'></div>

ts.html

<div class='notification-bar'></div>
<div class='header-bar'></div>

<div class='convo'>
  <div class='incoming sms msg unencrypted'>
      <span class='avatar'></span>
      <span class='bubble'>
          As incoming unencrypted SMS.
          <span class='metadata'>1:06pm</span>
      </span>
  </div>
  <div class='outgoing sms msg unencrypted'>
      <span class='bubble'>
          An outgoing unencrypted SMS.
          <span class='metadata'>1:16pm</span>
      </span>
  </div>
  <div class='incoming sms msg encrypted'>
      <span class='avatar'></span>
      <span class='bubble'>
          An incoming encrypted SMS.
          <span class='metadata'>1:26pm</span>
      </span>
  </div>
  <div class='outgoing sms msg encrypted'>
      <span class='bubble'>
          An outgoing encrypted SMS.
          <span class='metadata'>1:36pm</span>
        </span>
  </div>
  <div class='incoming push msg encrypted'>
      <span class='avatar'></span>
      <span class='bubble'>
          An incoming push message.
          <span class='metadata'>1:56pm</span>
      </span>
  </div>
  <div class='outgoing push msg encrypted'>
      <span class='bubble'>
          Push messages are always encrypted.
          <span class='metadata'>1:46pm</span>
      </span>
  </div>
</div>

ts.scss

// ----
// Sass (v3.3.0.rc.5)
// Compass (v1.0.0.alpha.18)
// ----

/* how wide should the windows/screens be? */
$width: 480px; // background image is 630px
$green: #64a926;
$blue: #3a7ef2;

.convo { background-color: #eeeeee; }
.bubble { 
  background-color: #fafafa;
  color: #333333; 
}
.metadata { color: #cccccc; }

.incoming .bubble {
  background-color: #ffffff;
}
.sms .bubble {
    border-color: $green;
}

.push .bubble {
    border-color: $blue;
}
.sending .bubble  { opacity: 0.7; }

.encrypted.msg { @extend .light-blue-background; }

.key-exchange {
  @extend .light-blue-background;
  padding-bottom: 1em;

  div {
  margin-top: 2em;
  height: 1em;
  padding-bottom: 1em;
  border: 1px solid #ddd;
  border-width: 1px 0;
  font-size: 0.5em;
  text-align: center;
  vertical-align: top;
  text-transform: uppercase;
  color: #aaa;
    
  .lock {
    background: url(https://raw.github.com/WhisperSystems/TextSecure/master/res/drawable-hdpi/icon_lock.png) no-repeat;
    background-position: center 40%;
    background-size: 60%;
    @extend .light-blue-background;
    display: inline-block;
    width: 4em;
    height: 4em;
    border-radius: 4em;
    border: 1px solid #ddd;
    margin: -1em 1em 0;
  }
  }
}

/* Style variants */
.green-stripe { border-top: 0.3em solid #64a926; }
.blue-stripe  { border-top: 0.3em solid #3a7ef2; }
.green-background { background: #64a926; }
.light-green-background { background: #d9e6cf; }
.blue-background  { background: #3a7ef2; }
.yellow-background  { background: #fff6df; }
.light-blue-background { background-color: #dfe8f7; }
.bluish { background-color: #d0d0da; }

/* Formatting */
.msg-text {
  display: block;
  padding: 0.5em 0.6em 0em;
}

.metadata {
  display: block;
  font-size: 0.70em;
  padding: 0.2em 0.6em;
}

.convo {
    width: $width;
    font-family: sans-serif;
    font-size: $width * 14 / 330;
    line-height: 1.2em;
}

$avatar-size: $width * 37 / 330;
.avatar {
  display: inline-block;
//  background: url(http://placekitten.com/g/200/300/);
  background: url(https://whispersystems.org/assets/header/raven-46e547e5d71484be52060be1155f6ff2.png) 30% 10%;
  background-size: 200%;
  width: $avatar-size;
  height: $avatar-size;
  border-radius: $avatar-size;
  float: left;
}

.bubble {
  position: relative;
  border-radius: ($width * 3 / 330);
  max-width: 75%;
  border-bottom: ($width * 3 / 640) solid #dddddd;
}

.incoming .bubble {
  float: left;
  &:after {
    content: '';
    display: block;
    position: absolute;
    width: 0;
    height: 0;
    top: 1em;
    left: -0.8em;
    border-right: solid 0.5em #ffffff;
    border-top: solid 10px transparent;
    border-left: solid 0.4em transparent;
    border-bottom: solid 10px transparent;
  }
}
.outgoing .bubble {
  float: right;
  
  &:after {
    content: '';
    display: block;
    position: absolute;
    width: 0;
    height: 0;
    top: 1em;
    right: -0.8em;
    border-left: solid 0.5em #ffffff;
    border-top: solid 10px transparent;
    border-right: solid 0.4em transparent;
    border-bottom: solid 10px transparent;
  } 
}

.outgoing .bubble, .outgoing .metadata {
  text-align: right;
}

.msg { padding: 0.3em (8 * $width/ 330); }

.msg:after {
    content: '';
    display: block;
    height: 0;
    clear: both;
}

/* android elements */
.notification-bar {
    background: url(https://whispersystems.org/blog/images/textsecure2-imessage.png) no-repeat;   
    background-size: 100%;
    width: $width;
    height: $width * 45 / 630;
}

.header-bar {
    background: url(https://whispersystems.org/blog/images/textsecure2-imessage.png) no-repeat;
    background-size: 100%;
    background-position: 0px ($width * -24 / 330);
    height: $width * 82 / 630;
    width: $width;
}

.entry-bar {
    background: url(https://whispersystems.org/blog/images/textsecure2-imessage.png) no-repeat;
    background-size: 100%;
    background-position: 0px ($width * -543 / 330);
    height: $width * 85 / 630;
    width: $width;
}

.checkmark {
  display: inline-block;
  background: green url(https://github.com/WhisperSystems/TextSecure/blob/master/res/drawable-mdpi/check.png?raw=true) center;
  background-size: 90%;
  width: 1em;
  height: 1em;
  border-radius: 1em;
  border: 0.15em solid #ffffff;
  margin: 6% 62%;
}

/* debug styles */
/*
.convo { border: 1px solid red; }
.msg { border: 1px solid blue; }
*/